Implants with threads, for example self-tapping threads, for insertion/screwing into holes made in the bone/dentine are available in large numbers and designs on the open market and are described in the patent literature. Thus, for example, reference may be made to Swedish Patent Application 9603091-7 filed by the same Applicant filing the present patent application.
In this connection it is known to use different thread formations on implants. Thus, for example, it is already known to use implants with cone-shaped threads and to choose different conicities on one and the same implant. The methods for forming the holes in the bone/dentine are also already well known. In this connection, reference may be made, in purely general terms, to dental treatment by the Brånemark System®.
Some of the threaded implants are cylindrical, while others can have the said conical designs in order to imitate the tooth root which they are intended to replace. The implants are inserted into holes that have been drilled beforehand in the jaw bone. A cylindrical hole is drilled for cylindrical implants, and for conical implants a conical hole is prepared. The cited method using the Brånemark System® involves securing screw-shaped implants in the jaw bone. After a period of healing-in, normally about 3-6 months, the bone has grown in direct contact with the implant and the latter can then be used to support a prosthetic reconstruction. This is in most cases achieved by means of a so-called spacer element being attached to the implant, which can be done by a screw connection. A transfer cap is then attached to the top of the spacer upon so-called impression-taking, and the finished prosthetic reconstruction can thereafter be applied to the spacer.
From the known methods it is already known that good long-term results are obtained if the osteointegration between the bone and the implant can take place with a tight profile and small pitch of the threads in question. During the osteointegration, the bone tissue grows in direct contact with the implant. Upon fitting the implants, the said holes are drilled in the bone with great precision. In this connection it is already known to use tightening instruments which rotate at about 20-25 rpm.
In WO 97/25933 (PCT/US97/00332) it has already been proposed, especially in connection with hard dentine, that the body presenting the thread should be made non-circular (asymmetric) in its cross-section.
The purpose of the non-circularity is to reduce the friction between bone and implant on insertion of the implant. This is important mainly in the case of hard bone.